1. Field of the Invention
The present invention is related to a method for inspecting localized image and a system thereof, and more particularly to a method for inspecting a defect on an image of a mask/semiconductor element and an applied inspection system thereof.
2. Description of the Prior Art
How to inspect defects on a semiconductor element is one of the major subjects of a semiconductor process. A prior art method for inspecting defects includes capturing a scanned image of a semiconductor element, such as a scanning electron microscope (SEM) image, and then determining the presence of a defect of the semiconductor element in the scanned image.
A prior art method of cell-to-cell inspection is applied on a semiconductor element with repeated pattern, such as a memory chip. Referring to FIG. 1, a scanned image 1 includes a plurality of repeated patterns 11, and the method of cell-to-cell inspection is performed to compare differences between the repeated patterns 11 to determine the presence of a defect. However, the method of cell-to-cell inspection is not suitable to be applied on a semiconductor element without any repeated pattern.
Another prior art method of die-to-die inspection can be applied on a semiconductor element without repeated pattern, such as a logical chip. Referring to FIG. 2, scanned images 2 and 2′ include irregular patterns 21 and 21′, and the method of die-to-die inspection is performed to compare differences between the irregular patterns 21 and 21′ in different scanned images 2 and 2′ to determine the presence of a defect. However, inherent differences between the scanned images 2 and 2′ may cause a higher fault rate. For example, these dies may have no defect and yet images of different dies may still have variant gray levels, or distort differently due to their respective charge distributions, or topographies, etc. It is, therefore, difficult to determine the presence of a defect on an SEM image by the method of die-to-die inspection. Contrarily, the problem with the die-to-die inspection would be less likely to occur when using the method of cell-to-cell inspection because the probability of distortion on one die is relatively smaller.
It should be noted that the methods of cell-to-cell and die-to-die inspection each possesses its own advantages, but they can not be implemented simultaneously. Furthermore, the foregoing methods compare images between cells or dies without the basis of the original design, and therefore accuracy of inspection can not be improved efficiently.
Accordingly, it is highly desirable to provide a method for inspecting localized image with or without repeated patterns avoiding the foregoing drawback.